1. Field of the Invention
The present invention relates to an occupant detection apparatus including a buckle switch, a seat position sensor, and an occupant detection electronic control unit.
2. Description of Related Art
A modern vehicle is equipped with an occupant detection apparatus. A typical occupant detection apparatus includes a main electrode, an electrostatic sensor, and an, occupant detection electronic control unit (ECU). The main electrode is arranged inside a seat. The electrostatic sensor is connected with the occupant detection ECU and is configured to output a current or a voltage indicative of disturbance of weak electric field, which is generated between the main electrode and a vehicle body. A typical occupant detection apparatus further includes a buckle switch for detecting whether a seat belt is fastened or unfastened, and a seat position sensor for detecting a position of the seat along a front-rear direction. The buckle switch and the seat position sensor are connected with the occupant detection ECU.
JP-2006-88916A corresponding to US Patent Application Publication 2006/0069509 discloses a vehicular collision determination apparatus in which a buckle switch and a seat position sensor are connected with an occupant detection ECU. The collision determination apparatus determines an occurrence of vehicle collision in order to activate, for example, an occupant protection apparatus such as an airbag, a seatbelt pretensioner and the like. The collision determination apparatus sets a collision determination threshold by referencing a determination result regarding whether the seat belt is fastened or unfastened, and a determination result regarding whether the seat is in a front position or a rear position.
The inventor of the present application has found that a conventional technique involves the following difficulty. According to JP-2006-88916A (which corresponds to US Patent Application Publication 2006/0069509), in response to start of the vehicle through key operation, both of the buckle switch and the seat position sensor are placed in continuous operation, and a large operating current flows in the occupant detection ECU via the buckle switch and the seat position sensor. In order to reduce power consumption due to the operating current, the occupant detection ECU controls both of the buckle switch and the seat position sensor so that the both sensors are intermittently energized. However, when the occupant detection ECU causes the both sensors to be intermittently energized, a radio noise is generated from the occupant detection ECU. This radio noise causes a negative influence on another electronic apparatus mounted in the vehicle.